It is known that manufacturing semiconductor devices on a wafer entails a number of steps, inclusive of photolithography and etching, thin film deposition, and the use of ion implantation steps alternately performed in order to develop or build-up the semiconductor device or wafer. Typically, the photolithography steps include coating a wafer with a photoresist wherein an ultraviolet photosensitive organic material is utilized. The photoresist is exposed through a mask, after which the resist is developed. Next, the exposed photoresist is etched thereby leaving given exposed areas on the surface of the wafer. Following the foregoing steps, additional processing steps such as deposition, implantation or etching may be employed on the exposed areas.
In deposition processes, particularly in PECVD processes, it is necessary to periodically remove or clean deposition material from the chamber or reactor hardware. A fluorine-based plasma discharge is commonly used to remove dielectric material such as silicon dioxide (SiO2), silicon nitride (Si3N4), and silicon oxynitrides (SiON). During such fluorinated plasma cleaning, AlF3 (which is a by-product of the cleaning) grows on exposed internal PECVD chamber hardware by reaction of various fluorine species with the aluminum or aluminum based chamber parts. This accumulation of AlF3 on the chamber hardware alters the ensuing plasma chemistry and adversely impacts film deposition properties. In essence, the slow accumulation of AlF3 causes drifting film properties and process control problems. (Refer to publication by B. Smith, et al, J. Electrochem. Soc. accepted for November 2001.)
Eventually, the AlF3 must be removed in order to maintain film properties within some process window. Wet chemical cleaning is commonly used to restore PECVD chamber performance (since AlF3 is water soluble). However, wet cleaning unfortunately involves removing the PECVD chamber from operation, disassembling the chamber, and cleaning the chamber parts in a wet chemical bath. This wet chemical cleaning unfortunately creates considerable chamber downtime during the wet cleaning procedure.
In the past, H2 plasma etching of AlF3 films on wafers has been demonstrated by S. G. Pearton, et al, Mat. Res. Soc. Symp. Aoc., Volume 282 (1993), p. 131. Pearton et al used H2 plasma to remove AlF3 etch-stop layers in GaAs-based wafer processing.
U.S. Pat. No. 5,882,489 disclose processes for cleaning and stripping photoresist from surfaces of semiconductor wafers. The process entails ashing the organic resist from a device, rinsing the device in water, and sputtering the rinsed device to remove residual contaminants. The stripping step is a dry etching process such as a microwave downstream process, a RIE process, or sequential or simultaneous microwave downstream and RIE process, wherein the rinsing step is performed with deionized (DI) water, and the sputtering step is performed with argon. The process is especially useful for etching via holes when the holes penetrate a conductive layer and create insoluble, inorganic contaminants such as AlF3.
A method for etch rate enhancement by background oxygen control in a soft etch system is disclosed in U.S. Pat. No. 6,143,144. This sputter etch cleaning process to remove or sputter off particles from the substrate surface within the processing chamber is accomplished by:
positioning a first substrate to be processed within a processing chamber, the first substrate including a material layer containing oxygen;
introducing a process gas into the chamber;
inductively coupling electrical energy to the process gas in the chamber to form an ionized gas plasma in the chamber;
positioning a second material substrate proximate the first substrate in the processing chamber;
biasing the first and second substrates with RF electrical energy so that the plasma etches the first substrate material layer and the second substrate, the material etched from the first substrate material layer producing activated oxygen in the gas plasma;
the second substrate being formed of a material which reacts with activated oxygen to form a stable oxygen-containing compound such that material etched from the second substrate reduces activated oxygen in the gas plasma;
whereby residual oxygen in the processing chamber is reduced to maintain an etch rate for subsequent sputter etching processes.
U.S. Pat. No. 5,017,403 disclose the use of plasma-enhanced chemical vapor deposition (PECVD) to form dielectric films. The process entails:                (a) providing a substrate in a chamber;        (b) flowing a reactant gas in the chamber;        (c) generating a plasma between the electrodes by R.F. power to dissociate the gas and deposit a predetermined planarization layer of carbonaceous material on the substrate; while maintaining the substrate at a relatively low temperature wherein the layer is soft as deposited and is then hardened by thermal or plasma treatment.        
A low pressure and low power Cl2/HCl process for sub-micron metal etching is disclosed in U.S. Pat. No. 5,976,986. The method entails:
placing aluminum metallization coated on at least one surface with a barrier layer in an etch chamber;
creating a transformer coupled plasma from Cl2, HCl, and an inert gas within the etch chamber, without a magnetic field, using separately powered electrodes positioned above and below aluminum metallizations wherein each of the electrodes are powered by less than 350 Watts, and wherein the pressure in the etch chamber is less than 15 milliTorr;
etching the aluminum metallizations with ions and radicals formed in the plasma; and adjusting a concentration of the Cl2 in the plasma during the creating and etching steps between a first higher concentration during etching of the aluminum metallization and a second lower concentration during etching of the barrier layer.
The addition of hydrogen to plasma is used to reduce corrosion during the etching of aluminum layers.
In the art of PECVD processing where fluorinated plasma discharges are utilized, there is a need to remove unwanted residues from PECVD chamber hardware without wet cleaning the chamber (i.e., disassembling the chamber and cleaning the chamber parts in a wet chemical bath), which results in considerable chamber downtime.